The project attempts to achieve the following objectives: 1) perform joint and muscle force analysis of elbow joint under various isometric functions, 2) calculate the forces in the ligaments and on the joint contact surface, 3) correlate the calculated muscle forces with the quantitative EMG measurement to verify the method and results of solutions, 4) examine the role of ligaments to the elbow joint stability. The mechanical contribution of each muscle to the joint function will be established based on both the direct load measurement method and the biplanar X-ray technique. An optimization method with proposed muscle force distribution principle will be used to verify the solution technique and results. The contact area of elbow joint under various loading conditions will be obtained by CT-7000 tomography. Finally, the contribution of ligaments to the joint stability will be studied by the displacement method on the loading apparatus.